/Engine/Plugins/Online/OnlineServicesEOSGS/Source/Public/Online/OnlineServicesEOSGSTypes.h
This method requires a Callback (lambda / function pointer) which will be called by the EOS callback with the CallbackInfo.
namespace UE { namespace Online { template<typename TEOSHandle, typename TEOSParameters, typename TEOSFn, typename TCallback> decltype(auto) UE::Online::EOS_Async ( TEOSFn EOSFn, TEOSHandle EOSHandle, const TEOSParameters & Parameters, TCallback && Callback ) } }